1. Field of Invention
This invention relates generally to powder-actuated fastener setting tools adapted to drive fasteners such as nails or pins, into concrete or other forms of masonry, and more particularly, to a cartridge strip magazine adapted to cooperate with the tool carrying a row of cartridges to be fed successively into the breech of the tool.
2. Status of Prior Art
Known types of powder-actuated fastener setting tools, such as the tool disclosed in the Popovich et al. U.S. Pat. No. 5,273,198, are provided with a forwardly-biased barrel slidable within a cylindrical housing. For reasons of safety, the tool is operable only when the muzzle of the barrel is pressed against a concrete surface to advance the breech of the barrel rearwardly whereby when the cartridge then in line with the breech is fired, the resultant explosive force acts to propel a driving piston to launch a fastener.
In a powder-actuated tool of the type disclosed in the Burdick et al. U.S. Pat. No. 4,565,114, the breech of the tool has a conical inlet and the tool includes a magazine feed channel perpendicular to the main axis of the tool. This channel accommodates a cartridge strip magazine, allowing this magazine to successively place the cartridges carried by the magazine in alignment with the breech in readiness to be fired.
As noted in the Burdick patent, it has long been the practice in cartridge strip magazines for a powder-actuated fastener setting tool to socket each cartridge in a frusto-conical shroud formed of resilient plastic material projecting from the strip. This plastic shroud which nests within the conical inlet of the breech of the tool has the same or a greater cone angle. An advantage of this plastic shroud is that because of its resilience, it will self-eject and not require a mechanical ejector.
But the main drawback of a conically-shrouded multiple round magazine of this known type is that it has a tendency to misfire or leak gas. The leakage of gas reduces the effective explosive force produced when a cartridge in alignment with the breech is fired. In order to drive a fastener fully into hard concrete or other masonry that is difficult to penetrate, it is essential that the available explosive force be fully exploited.
To obviate this drawback, Burdick provides a cartridge strip magazine for a powder-actuated tool having a row of non-conical, stepped plastic shrouds or projections which create cartridge-receiving sockets at spaced positions along the strip. When a non-conical, stepped projection carrying a cartridge is nested within the frusto-conical inlet in the breech of the tool, the leading edges of the multi-stepped projection make contact with the conical surface of the breech inlet to produce a series of spaced plastic sealing rings. These rings prevent the expanding gas generated when the cartridge is fired, from leaking out through the space between the breech inlet and the stepped projection nested therein.
The Burdick series of plastic sealing rings which make point contact with the conical wall of the breech inlet at spaced positions along the wall do not assure the total avoidance of gas leakage, for each point contact seal can be overcome by the high-pressure expanding gas produced by the exploding powder.
It must be borne in mind that when the cartridge powder is exploded, the resultant expanding gas is confined to the small breech region between the cartridge and the driving piston in the barrel. At the instant of the explosion, the pressure of the gas in this confined region is enormous, and it is then capable of bypassing even a strong gas seal.